Many systems have been proposed for testing nut runner torque control. A problem exists in torque control over a wide range of varying joint rate. Joint rate may be defined as the relative amount of rotation required to bring the threaded fastener to its final torque after the fastener has been seated. Very hard joints require little rotation. Soft joints require considerably more rotation to achieve the desired torque. Thus, a device for testing the torque output of a nutrunner should be capable of simulating the joint rate response of different threaded fasteners. A low joint rate or slow torque buildup is typical of a gasketed joint, and a high torque rate or rapid torque buildup is typical of metal to metal connections employing threaded fasteners.
Most test devices to date have employed a threaded fastener in the simulated joint. This introduces the variable of friction in any determination of applied torque. This variable results in scatter of torque results, and additionally the fastener must be backed off after each run. This is, of course, time consuming. The test apparatus should have much less scatter than the device to be tested to provide a good reliable test. Threaded joints generally exhibit too much scatter for testing modern tools.
A recent improvement in test joints has employed the use of a torsion bar spring and a fast acting brake. This simulates a hard joint quite well. However, to date, attempts to simulate a soft joint have been only moderately successful and lack the degree of variability desirable in a test joint apparatus. In the past, most means of simulating soft joints have consisted of rubber torsion tubes and/or steel coil springs. These devices suffer generally from secondary vibration modes and short cycle life. In addition, their use requires additional components in the test joint.
The object of the present invention is to provide a variable rate test joint which is simple, reliable, accurate, reproducible, and easy to use.
It is a further object of the present invention to utilize an interchangeable solid torsion bar to simulate various, fixed hard joint rates and to utilize a modulated air brake in combination with the torsion bar to simulate soft joint rates.
It is a further object of this invention to provide a means for measuring the torque applied to the test joint.
It is a further object of this invention to prevent the joint from unwinding once the torque applying device is shut off to prevent possible damage to the tool being tested.
It is a further object of this invention to provide a means for manually checking by means of a beam torque wrench or similar device the accuracy of the applied torque.
It is a further object of this invention to produce a variable rate test joint which is economical to build, operate, and maintain.
These and other objects are obtained in an apparatus comprising: a support, a brake attached to the support, a one-way clutch attached to the support and spaced apart from the brake, a torsion spring engaged with and mounted between the brake and the one-way clutch for rotation with the clutch and the brake, a means for actuating the brake, and a means for measuring torque applied to the torsion spring at its one-way clutch engaging end.